1. Field of the Invention:
The present invention relates to a valve timing control apparatus, which controls valve timing of a valve that is opened or closed by a camshaft through transmission of a torque from a crankshaft of an internal combustion engine.
2. Description of Related Art:
A previously known valve timing control apparatus includes a housing, which is rotated together with a crankshaft, and a vane rotor, which is rotated together with the camshaft. This valve timing control apparatus controls the valve timing through use of hydraulic fluid, which is supplied from a supply source (e.g., a pump) upon rotation of the engine. For instance, the valve timing is controlled by changing a rotational phase of the vane rotor toward an advancing side or a retarding side relative to the housing by guiding the hydraulic fluid, which is supplied from the supply source, into an advancing chamber or a retarding chamber, which are partitioned with a vane of the vane rotor in the housing.
Japanese Unexamined Patent Publication No. 2002-357105A (corresponding to US2002/0139332A1) teaches such a valve timing control apparatus. In this valve timing control apparatus, a limiting member, which is received in the vane rotor, is moved into a recess formed in an inner surface of the housing before the time of stopping the engine. Thereby, at the time of executing the next engine start, the rotational phase is limited to a limited phase, which is between the most advanced phase and the most retarded phase, to ensure the required startability of the engine. In the case of the valve timing control apparatus recited in Japanese Unexamined Patent Publication No. 2002-357105A (corresponding to US2002/0139332A1), when the engine is instantaneously stopped due to an abnormality, the engine may be restarted in a state where the limiting member is not received in the recess. Thus, in such a case where the limiting member is not received in the recess at the time of engine stop, it is required to move the limiting member into the recess within the engine start period. However, when the working fluid remains in the working chamber before the engine start, the limiting member, which receives the pressure of the hydraulic fluid supplied into the working chamber in the direction away from the recess, needs to be moved in the inserting direction toward the recess while pushing the remaining hydraulic fluid out of the working chamber during the engine start period. Therefore, under the low temperature environment, in which the viscosity of the working fluid is increased, the movement of the limiting member into the recess cannot be made in time, so that the startability of the engine is disadvantageously deteriorated.
In view of the above disadvantage, the inventor of the present invention has proposed to limit the rotational phase by using two types of limiting members and two types of resilient members in Japanese Patent Application No. 2009-193566 (corresponding to WO/2010/029740A1). Specifically, in the valve timing control apparatus recited in Japanese Patent Application No. 2009-193566 (corresponding to WO/2010/029740A1), when the engine is stopped before the time of moving a primary limiting member (i.e., one of the two limiting members) into the recess formed in the inner surface of the housing, the pressure, which is introduced into the working chamber, is reduced. Therefore, the secondary limiting member (i.e., the other one of the two limiting members) is urged by the corresponding secondary resilient member and is thereby moved into the recess. The primary limiting member, which is engageable with an engaging portion of the secondary limiting member, is urged against the engaging portion of the secondary limiting member by the corresponding primary resilient member in the inserting direction thereof together with the secondary limiting member. In this way, at the rotational phase, which is different from the limited phase, the primary limiting member contacts the inner surface of the housing in the removed state of the primary limiting member where the primary limiting member is removed out of the recess.
Even when the primary limiting member is engaged with the inner surface of the housing through this engagement, the secondary limiting member, which is urged by the secondary urging member, pushes the remaining working fluid, which remains in the working chamber, and the engaging portion of the secondary limiting member is spaced from the primary limiting member. Therefore, in the next engine start period, when the rotational phase is changed to the limited phase to move the primary limiting member into the recess through use of an oscillating torque, which is generated by cranking of the engine, the primary limiting member can be quickly moved in the inserting direction. As a result, even in the low temperature environment, the primary limiting member can be quickly moved into the recess to limit the rotational phase at the limited phase, so that the startability of the engine can be ensured.
In the case of the valve timing control apparatus, which is recited in Japanese Patent Application No. 2009-193566 (corresponding to WO/2010/029740A1), the primary limiting member and the secondary limiting member are slidably received in the receiving hole of the housing, and the primary limiting member is slidably received in the secondary limiting member, which is configured into the tubular form. In the case of the above construction, when the slide gap between each of the primary and secondary limiting members and the receiving hole and the slide gap between the primary limiting member and the secondary limiting member are both increased, the correct orientation of each of the primary and secondary limiting members cannot be maintained, so that the primary limiting member may possibly be tilted or may experience an inserting malfunction (i.e., the primary limiting member being not appropriately inserted into the recess due to an interference with the tilted secondary limiting member). In contrast, when the slide gap between each of the primary and secondary limiting members and the receiving hole and the slide gap between the primary limiting member and the secondary limiting member are both decreased, the primary limiting member and the secondary limiting member may possibly interfere with each other due to the presence of the manufacturing tolerance. Also, a shearing resistance is applied to each of the primary and secondary limiting members due to the presence of the working fluid, which enters the slide gap that is adjacent to the working chamber, so that the movement of the primary and secondary limiting members may possibly be interfered. Particularly, at the time of moving the primary limiting member, which is engaged with the inner surface of the housing, into the recess to execute the engine start, when the inserting speed (moving speed) of the primary limiting member in the inserting direction is decreased due to the interference and/or the presence of the shearing resistance, the primary limiting member may possibly not be entered into the recess in time within the engine start period.